A mold closer is described in German patent document DE-A1 37 22 340 for synchronously displacing the two mold halves toward and away from one another for the production of articles from thermoplastic synthetic resins. The apparatus described in this publication has at least one draw rod and a pressure rod, between the ends of which respective yokes are connected, the yokes forming a frame. The draw rod and the pressure rod are mutually parallel and extend in the displacement direction while the yokes extend transversely to this direction and mounting plates are provided to carry the respective mold halves which are displaceable by this mechanism toward and away from each other.
One of the yokes has a cantilever arm which directly engages one of the mold-mounting plates while the other yoke acts upon the second mold-mounting plate through a force-transmitting mechanism. The force-transmitting mechanism is provided on a frame which is suspended from a spatially-fixed housing formed with guide beams separate from the frames and enabling separate movements of the frames. As a consequence the mechanism generating the closing force and the guides for the mold-mounting plates can be decoupled from one another and hence the frame which is affected by the force-transmitting mechanism or carries the latter can be free to deform without affecting the guidance of the mold-mounting plates.
However with this system a precisely synchronous displacement of the mold-mounting plates may not be guaranteed since the mechanism generating the closing force may not act exactly symmetrically on both of the mold-mounting parts.
The synchronous action, moreover, is generated by a hydraulic or pneumatic piston-and-cylinder arrangement which frequently permits a shift in the predetermined calibration position at which mold closing is to occur.
The mold-closing apparatus can, of course, be mounted on a carriage or like transporter which enables the entire mold assembly to shift between, for example, an extrusion station at which a parison can be produced and the blowing station.
As a general matter, moreover, the earlier mold-closing mechanisms, to the extent that they have attempted to ensure synchronous displacement of the mold halves and a precise mold-closing position, have been relatively massive and complex. Moreover, in mold-closing systems of this type it has been difficult to ensure that the mounting plate for a mold half which is relatively distal to the force-generating unit is acted upon symmetrically to the mold-carrying plate which is proximal to that unit. As a result, either deformation of the guiding or guided members could not be entirely avoided or significant structure was required to minimize such deformation.